The Data-Over-Cable Service Interface Specification (DOCSIS) was established by cable television network operators to facilitate transporting data packets, primarily internet packets, over existing community antenna television (CATV) networks. In addition to transporting data packets, as well as television content signals over a CATV network, multiple services operators (MSO) also use their CATV network infrastructure for carrying voice, video on demand (VoD) and video conferencing packet signals, among other types.
Broadband services can be delivered via existing cable infrastructure from MSOs, digital subscriber lines (xDSL), integrated service digital network (ISDN), public switched phone networks, or T1 connections from telecommunications operators or internet service providers, satellite from satellite operators, or wireless services (such as, e.g., cellular, 802.11 or Wi-MAX standards, etc.) from wireless service providers, among many others. In some DOCSIS implementations, a modular cable modem termination (M-CMTS) architecture can be comprised of components such as, for example, an M-CMTS core, Edge-QAM (EQAM), upstream receiver and DOCSIS Timing Interface (DTI) server. The M-CMTS architecture can provide operators with increased efficiency and availability of network resources.
An element of the communication system architecture is the separation of a downstream physical layer QAM modulation and up-conversion functions from a traditional CMTS to EQAMs and upstream receivers. The separation allows the EQAM to support both video and DOCSIS standards thereby facilitating operators using the same network resources to support multiple types of services such as, for example, data, voice and video.
The interface supporting the separation of a broadband communication system (e.g., M-CMTS core) and modulator/demodulator systems (e.g., EQAM(s)/upstream receiver(s)) is defined by the DOCSIS standards as a Downstream External PHY Interface (DEPI), which provides for transport of downstream data between M-CMTS core and EQAM(s) and the transport of upstream data between the upstream receiver(s) and M-CMTS. A component of the DEPI interface is a DTI server, defined by the DOCSIS Timing Interface Specification (DTI) which can provide the exchange of timing messages between a DTI sever and DTI clients (e.g., M-CMTS core, EQAM(s) and upstream receiver(s)) to synchronize timing between the devices.